Maintain Access Strip Technique (MAST) crown: a novel technique to stabilize anterior teeth while maintaining pulp canal access

Background

The anterior tooth that has suffered significant trauma often requires endodontic treatment for future maintenance and function.¹ For patients, such trauma can be physically uncomfortable and both functionally and aesthetically unpleasant. Studies have shown that dental trauma can affect the quality of life of both children² and adults.³ Therefore, the goal of a clinician managing such an initial presentation of trauma in an emergency setting should be to restore function, appearance and ensure the patient remains asymptomatic prior to long-term definitive treatment.

A key objective of the initial management of a dental trauma causing irreversible pulpal damage or pulpal necrosis is to effectively commence appropriate endodontic treatment.⁴ This requires the clinician to suitably isolate a tooth with rubber dam,⁵ then ensure that there is an effective intra-appointment coronal seal.⁶ In a tooth that has been severely traumatized, or that has suffered extensive restorative failure, isolation and temporization can be challenging to achieve.

This novel technique has been developed to allow quick and effective restoration of teeth, while maintaining ease of access to the pulp canal for further endodontic treatment. In situations where pulpal prognosis is unclear, use of available literature such as the guidance from the International Association of Dental Traumatology (IADT)⁷ should be used as part of the clinician's decision-making process. The MAST crown approach can be used to manage both traumatized or extensively broken-down teeth in these instances.

The MAST crown technique draws inspiration from previous literature regarding the use of canal projection with gutta percha points.^8,9,10,11 However, the novelty of this approach is the use of an anatomical strip crown concurrently with the canal projection technique to develop a stable, aesthetic and functional build-up of the tooth. The authors acknowledge this is the first time this technique has been described.

MAST crown method

Step 2

Adjust the strip crown with scissors to form a predictable shape and seating position (Figure 1). Only a minimal collar should extend beyond the margins of the tooth when fully seated. Two small drainage holes towards the incisal edge can be punctured using a straight probe. This allows excess composite to flow outwards when seating.¹³

Step 4

Insert the GP cone into the exposed canal to ensure it will fully seat (Figure 2). If the diameter of the canal is far greater than the GP cone, consider cutting the cone higher up at a broader taper. Compare the size of your bur to the cut end of the GP cone – this should be similar in size. Place the shell crown back into position on the tooth requiring build up, and note where the optimal endodontic access would be sited – this is likely to be on the palatal aspect of the strip crown (Figures 3 and 4).¹⁴

Step 5

Extra-orally, use the diamond bur to make a small hole in this position on the strip crown. Confirm the GP cone will pass through this and there is not a significant discrepancy in size between the prepared access and the selected GP cone (Figure 5). Remove the GP cone and apply petroleum jelly along the length of the cone. Use a cotton wool roll to remove any excess, to leave only a very thin film of jelly. This will prevent mechanical retention of the composite to the GP cone when cured. With the GP cone situated back into position in the modified crown form, reposition this on to the traumatized tooth. Ensure full seating of the shell crown and that the GP cone seats fully into the exposed canal forming a canal projection (Figure 6).

Step 6

Carry out an appropriate bonding protocol for composite on the tooth requiring build up. At this stage the clinician should preload the modified strip crown with composite (Figure 7), seat fully onto the tooth ensuring the GP cone is located in the orifice to sufficient depth (Figure 8) and cure the composite.

Step 7

Remove the GP cone with tweezer forceps, and the strip crown with an excavator or similar hand instrument This can be aided by using a scalpel to weaken the strip crown if the neck is narrower than the maximum bulbosity of the restoration. The tooth is now restored in composite with access maintained (Figures 9 and 10). Use polishing instruments to remove excess composite from the margins. If rubber dam isolation was not possible earlier, it can now be placed to isolate the tooth.

At this stage, the clinician can decide to continue with root canal treatment, or temporarily dress the tooth through the now developed and maintained endodontic access. If access through the composite is too narrow, it can safely be enlarged using a non-end cutting endodontic bur or a standard tapered bur. The access hole can be used as a pilot hole.

Discussion

Having a sound intra-appointment restoration is crucial for maintaining a good endodontic seal¹⁵ and can provide support for any further management of trauma, for example splint placement. A sound restoration can also improve the patient's confidence and function.

The use of a strip crown to restore fractured or broken anterior teeth has been cited in dental literature.¹⁶ Restoring a tooth prior to root canal treatment can create additional challenges for a clinician incurring the risk of iatrogenic damage and further tooth tissue loss when re-accessing the tooth.¹⁷ The existing approaches are: free-hand build up with composite with or without canal projection techniques, or dressing the tooth. Free-hand build up can be time consuming and effective isolation can be challenging following a large-scale trauma. Dressing the tooth does not improve the patient's functional or aesthetic concerns and provides no support for splinting if required.

The MAST crown approach aims to reduce the challenges of managing a broken anterior tooth by restoring function and aesthetics, allowing ease of access to the pulp chamber and system and facilitating correct isolation using rubber dam. This allows the clinician to effectively undertake the process of chemical cleaning and disinfection of the canal network.¹⁸ The technique is straightforward and with most of the preparation occurring outwith the patient's mouth, reduces the intra-oral time required for isolation and bonding of composite material. Minimizing time spent maintaining a clear and isolated operating field is of great benefit to patients who are psychologically affected following trauma¹⁹ or in cohorts who may not be able to cooperate for extended treatment appointments.²⁰

The use of the strip crown to form the anatomical shape of the restoration enables quick and straightforward finishing and polishing of the composite, which is vital in the perceived cohorts of patients for whom the MAST crown approach would be likely to be suitable.

Case report

An 11-year old child attended for an emergency appointment at a paediatric dentistry department within a dental teaching hospital, between planned endodontic treatment appointments for their UR1. Their reason for attendance was the failure of the existing interim resin composite restoration (Figures 11 and 12), which had been built up free-hand with a subsequently prepared palatal access cavity sealed with glass ionomer cement. This had caused some distress to the child and their parent owing to the extent of tooth structure missing following an enamel–dentine pulp fracture in an immature tooth, which had subsequently lost vitality. The definitive endodontic treatment for the tooth had been planned to be completed at an upcoming appointment of suitable length.

Approach

With local anaesthesia achieved, the MAST crown approach was followed to stabilize the tooth effectively as an intermediate restoration. At this stage, rubber dam was then placed, the canal was irrigated with sodium hypochlorite passively with an endodontic syringe, then dried with paper points. Non-setting calcium hydroxide paste and sterile cotton wool were placed into the canal and pulp chamber and then glass ionomer cement was used to seal the developed access. The patient returned for a further appointment, and apexification with an apical MTA plug was performed.

Using the MAST crown approach in this case allowed for an efficient use of the clinician's time to stabilize the tooth with a functional and aesthetic restoration between treatment appointments (Figures 13–16).

Conclusion

The MAST crown approach is a novel, time-saving and effective method allowing clinicians to restore a severely broken or traumatized tooth, while maintaining endodontic access for root canal treatment. This technique is applicable for traumatized or damaged teeth where there is irreversible pulpal damage, or pulpal necrosis present, or where endodontic treatment has previously been initiated. It is hoped that, in time, this technique will become a valuable addition to the dental clinician's armamentarium.